Ultrasmall Ink Droplets Trap Light on Photonic Crystal

EuroPhotonicsMar 2018
CAMBRIDGE, England — A microscopic 'pen' has been developed that uses a commercially available printing technique to write nanostructures that are small enough to trap and harness light. The use of inkjet printing in nanophotonics has so far been limited by the coarse resolution of conventional printing methods.

Researcher Vincenzo Pecunia at the University of Cambridge, whose work focuses on printable optoelectronic materials, obtained an electrohydrodynamic jet printer for his team. A chance meeting between Pecunia and researcher Frederic Brossard at the Hitachi Cambridge Laboratory led to the discovery that this ultrahigh-resolution printer could print structures small enough to be used in nanophotonics.

In a hybrid approach for creating and fine tuning high-Q nanocavities, the researchers locally deposited organic ink droplets from the electrohydrodynamic printer onto the surface of an inorganic 2D photonic crystal template.

Light trapped by a tiny droplet on a photonic crystal surface. The droplet has been printed by a super high-resolution inkjet printer. Courtesy of University of Cambridge and Hitachi Cambridge Laboratory.These ultrasmall droplets could be 'drawn' on the crystals as if from a very fine pen, and could change the properties of the crystals so that light could be trapped. The researchers were able to create many different patterns onto the photonic crystals, at high speed and over a large area. They also found that they could make patterns from all sorts of printable materials using this method. They found the method to be scalable and low-cost. Further, they found that the photonic crystals were reusable because the ink could be washed away.

“Previous efforts to combine these two areas had bumped into the limitations of conventional inkjet printing technology, which cannot directly deposit anything small enough to be comparable to the wavelength of light,” said Pecunia. “But through electrodynamic inkjet printing we've been able to move beyond these limitations.”

To show the controllability of their method researchers tuned the resonance of the printed nanocavities by the number of printer passes, and fabricated photonic crystal molecules with controllable splitting.

The demonstration of nanocavities obtained by surface deposition on a blank photonic crystal introduces a novel method for a free-form, high-density, material-independent, high-throughput fabrication technique that could be used in a range of photonic applications.

“This fabrication technique opens the door for diverse opportunities in fundamental and applied sciences,” said Brossard. “A potential direction is the creation of a high density of highly sensitive sensors to detect minute amounts of biomolecules such as viruses or cancer cells.”

Brossard said that the device could also be used to study phenomena requiring very strong interaction between light and matter in new materials, and to create lasers on demand.

“Finally, this technology could also enable the creation of highly compact optical circuits which would guide the light and which could be modified by inkjet printing using the photonic crystal template,” he said.